1. Field of the Invention
The present invention relates to an ink jet printing or recording apparatus. In particular, the invention concerns the ink jet printing apparatus for producing records by using ink droplets of smaller particle size among those produced from ink ejection by a nozzle.
2. Description of the Prior Art
In the ink jet printing apparatus, pressurized ink is supplied to a nozzle which is vibrationally energized by an electro-strain element excited electrically from a power supply source of high frequency, whereby ink droplets are ejected through a nozzle orifice. The ink droplets thus ejected are then electrically charged or electrified in accordance with information signals to be recorded and subsequently caused to run through an electric field of a predetermined intensity. As a result, the ink droplets are deflected in dependence on the electric charge carried by them and impinge on a recording medium to produce thereon an intended record or records. The recording or printing apparatus of this type is known and referred to as the ink jet printing or recording apparatus of charge modulation type.
In the ink jet printing apparatus of the charge modulation type, it is possible to produce alternately the ink droplets of a large diameter and a small diameter by setting appropriately the conditions for generation of ink droplets such as pressure under which ink is supplied to the nozzle, intensity or magnitude of excitation imparted to the nozzle, frequency of the excitation and so forth.
There has been already proposed a recording system in which record is produced by utilizing the ink droplet of a smaller diameter (hereinafter referred to also as ink droplet of small size or simply as small size droplets) which is imparted with quantities of electric charge in dependence on the information signals supplied from an information signal source. For example, reference is to be made to U.S. Pat. No. 4,016,571 specification of Takahiro Yamada issued Apr. 5, 1977 and assigned to the same assignee as the present application.
Since the system recited above allows ink droplets of a very small diameter (about one-third of the diameter of large size ink droplet) to be produced from a relatively large nozzle orifice, not only the work for fabricating the nozzle orifice is much facilitated and the orifice thus scarcely suffers clogging, but also the recording with the ink particles of small size can be carried out with an enhanced reliability, whereby a high density recording of images, pictures, patterns and so forth can be accomplished with an improved quality, to advantage.
However, in order to actually assure the advantages described above, it is required that the small size ink droplets be produced stably and reliably from the nozzle and that the timing at which the small size ink droplet is separated (hereinafter referred to also as separation timing) has to coincide with phase of the information signal to be recorded.
In this connection, it has been observed that variations in the ambient temperature and humidity as well as operation or shut-down of the apparatus for a long period of time will bring about variations in the physical properties of ink contained in the nozzle and intensity of excitation applied to ink ejected from the nozzle, involving difficulties in producing the small size ink droplets stably and possibly in matching the separation timing of the small size ink droplet with the phase of the information signal.
In conjunction with the proposed system, it is also known to impart a predetermined quantity of electric charge to the small size droplets for detection thereof and establish the coincidence between the separation timing of the small size ink droplet and the information signal by utilizing the output signal from the charge detector. However, it is impossible to establish such coincidence automatically.